Method, apparatus and system providing holographic layer as micro-lens and color filter array in an imager

ABSTRACT

A method, apparatus, and system that provides a holographic layer as a micro-lens array and/or a color filter array in an imager. The method of writing the holographic layer results in overlapping areas in the hologram for corresponding adjacent pixels in the imager which increases collection of light at the pixels, thereby increasing quantum efficiency.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 13/914,784 filed Jun. 11, 2013, which is a continuation of U.S.patent application Ser. No. 13/333,245, filed Dec. 21, 2011, now U.S.Pat No. 8,476,575, which is a divisional of U.S. patent application Ser.No. 11/656,442 filed on Jan. 23, 2007, now U.S. Pat. No. 8,101,903, eachof which are incorporated herein by reference in their entireties.

FIELD OF THE INVENTION

Disclosed embodiments relate generally to a method, apparatus and systemproviding a micro-lens and/or color filter array in an imager.

BACKGROUND

Imaging devices, including charge coupled devices (CCD) andcomplementary metal oxide semiconductor (CMOS) sensors have commonlybeen used in photo-imaging applications. A CMOS imager circuit includesa focal plane array of pixels, each one of the pixels including aphotosensor, for example, a photogate, photoconductor or a photodiodefor accumulating photo-generated charge in the specified portion of thesubstrate. Each pixel has a charge storage region, formed on or in thesubstrate, which is connected to the gate of an output transistor thatis part of a readout circuit. The charge storage region may beconstructed as a floating diffusion region. In some imager circuits,each pixel may include at least one electronic device such as atransistor for transferring charge from the photosensor to the storageregion and one device, also typically a transistor, for resetting thestorage region to a predetermined charge level prior to chargetransference.

In a CMOS imager, the active elements of a pixel perform the functionsof: (1) photon to charge conversion; (2) accumulation of image charge;(3) resetting the storage region to a known state; (4) transfer ofcharge to the storage region; (5) selection of a pixel for readout; and(6) output and amplification of signals representing pixel reset leveland pixel charge. Photo charge may be amplified when it moves from theinitial charge accumulation region to the storage region. The charge atthe storage region is typically converted to a pixel output voltage by asource follower output transistor.

Exemplary CMOS imaging circuits, processing steps thereof, and detaileddescriptions of the functions of various CMOS elements of an imagingcircuit are described, for example, in U.S. Pat. No. 6,140,630; U.S.Pat. No. 6,376,868; U.S. Pat. No. 6,310,366; U.S. Pat. No. 6,326,652;U.S. Pat. No. 6,204,524; U.S. Pat. No. 6,333,205; and U.S. Pat. No.6,852,591, all of which are assigned to Micron Technology, Inc. Thedisclosures of each of the foregoing are hereby incorporated byreference in their entirety.

Semiconductor photosensors whether for a CMOS, CCD or othersemiconductor imager can be fabricated on a common semiconductorsubstrate to form a pixel array. Each photosensor is responsive toradiation to produce an output that is a measurement of the amount ofreceived radiation. An input optical device, such as a microlens arrayand/or an optical color filter array, are typically placed in theoptical input path of the input radiation to control or manipulate theradiation in order for the radiation to be properly received at thepixels of the pixel array and within a specified color wavelength range.There is desire and need for simplified and efficient method, apparatusand system to focus and color separate input radiation in an imager.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a first embodiment describedherein.

FIG. 2 is a schematic illustration of a second embodiment describedherein.

FIG. 3 is a schematic illustration of a third embodiment describedherein.

FIG. 4 is a schematic illustration of a fourth embodiment describedherein.

FIG. 5 is a schematic illustration of a written optical holographiclayer used to increase quantum efficiency.

FIG. 6 is a schematic illustration of a fifth embodiment describedherein.

FIG. 7 is a block diagram illustrating a CMOS imaging device containingembodiments described herein.

FIG. 8 is a block diagram illustrating a camera containing embodimentsdescribed herein.

DETAILED DESCRIPTION OF THE INVENTION

Disclosed embodiments relate to a method, apparatus and system providinga holographic layer as a micro-lens and color filter array in an imager.The embodiments discussed herein enable an imaging device to focus andseparate input radiation by using an optical holographic layer (OHL) forthe pixel array of the imaging device instead of a separate and distinctcolor filter array and microlens array.

As used herein, the terms “semiconductor substrate” and “substrate” areto be understood to include any semiconductor-based structure. Thesemiconductor structure should be understood to include silicon,silicon-on-insulator (SOI), silicon-on-sapphire (SOS),silicon-germanium, doped and undoped semiconductors, epitaxial layers ofsilicon supported by a base semiconductor foundation, and othersemiconductor structures. The semiconductor need not be silicon-based.The semiconductor could be other semiconductors including, for example,germanium or gallium arsenide. When reference is made to thesemiconductor substrate in the following description, previous processsteps may have been utilized to form regions or junctions in or over thebase semiconductor or foundation.

The term “pixel,” as used herein, refers to a photo-element unit cellcontaining a photosensor device and associated structures for convertingphotons to an electrical signal. For purposes of illustration, arepresentative three-color R, G, B pixel array is described herein;however, the invention is not limited to the use of an R, G, B colorarray. In addition, embodiments can also be used in a mono-chromaticarray where just one color is sensed by the array. Accordingly, thefollowing detailed description is not to be taken in a limiting sense.

It should also be understood that, taken alone, an imager pixel does notdistinguish one incoming color of light from another and its outputsignal represents the intensity of light received and corresponds toquantum efficiency for the given color. For purposes of this disclosure,however, a pixel of a pixel array will be referred to by color (i.e.,“red pixel,” “blue pixel,” etc.) when a color filter is used inconnection with the pixel to pass a particular wavelength of light,corresponding to a particular color, onto the pixel. For example, whenthe term “red pixel” is used herein, it is referring to a pixelassociated with a red color filter that filters wavelengths of lightwithin a wavelength range centered at about 650 nm to the underlyingpixel. Similar wavelength ranges exist for the “blue” and “green” pixelswhich are centered about a respective blue and green wavelength foreach. It is also to be understood that when the term “blue pixel,” “redpixel,” or “green pixel” are used herein, they refer to the wavelengthsof light coming to the pixel.

Moreover, while embodiments herein are described with reference to asemiconductor-based CMOS imager, it should be appreciated that theembodiments may be applied to any micro-electronic or micro-opticaldevice that requires high quality microlenses and/or color filters foroptimized performance. Other micro-optical devices that can employ theembodiments described herein include semiconductor CCD imagers, anddisplay devices as well where a pixel emits light.

Semiconductor image sensor arrays may be designed to providehigh-spatial-resolution sensing capability by implementing small sensingpixels. Each fundamental pixel includes a photosensitive element thatabsorbs input radiation to produce electric charges representative ofthe amount of received radiation. The radiation-induced charges are thenread out in form of an electric current or voltage to produce a pixeloutput. Various types of photosensitive elements may be used, includingbut not limited to, photodiodes, photo conductors, and photogatesensors.

For CMOS imagers, each active pixel generally includes a photosensor anda pixel circuit with several associated transistors that providein-pixel signal processing functions such as signal conversion, signalreset, and signal amplification and output. See e.g., U.S. Pat. No.7,026,596 to Fossum.

Image sensor arrays may be designed to produce monochromatic images orcolor images. In a monochromatic image, each pixel may be used toproduce an image pixel in the output image. Hence, the number of imagepixels in the output image is dependent on the number of pixels in thearray. A color image sensor array, however, typically uses three pixelsfor sensing different colors, e.g., red, blue and green with ademosaicing process to produce a multiple colored image pixel, e.g., athree-color pixel in the output image.

Disclosed embodiments provide an optical holographic layer (OHL) in animager/pixel array that is used to process input radiation for detectionby photosensors. The optical holographic layer is designed to operate asa microlens and/or as a color filter. The optical holographic layer maybe used, in place of a separate microlens array and/or a color filterarray, for focusing a spatial part of the input radiation on to apixel's photosensitive element and/or to filter different spectral bandsof received radiation to different pixels. This allows the pixel arrayto collect more light of pre-defined colors and thereby increases thequantum efficiency of the array by, for example, 2-10 times.Additionally, the use of the optical holographic layer decreasescross-talk between neighboring pixels.

An optical holographic layer is supposed to be optically refractive innature when interacting with input radiation. Notably, an opticalholographic layer may be fabricated in planar layer designs with surfacefeatures by using surface patterning techniques including those widelyused in semiconductor fabrication. In contrast to the conventionaloptical fabrication of a microlens, complex fabrication of curvedoptical surfaces is eliminated in the optical holographic layer. Inparticular, as described below, an optical holographic layer can beintegrated with other layers fabricated over a substrate containing apixel array. Hence, the fabrication of the optical holographic layer andfabrication of the pixels of the pixel array may be integrated with oneor more fabrication steps in a single fabrication process.

The optical holographic layer is formed of holograms, which may besimply optical grating patterns. In operation, the grating patternsbreak up a received input wave into multiple waves and combine themultiple waves into new waves with desired optical properties. Dependingon specific requirements of the application, the grating patterns may bedesigned to carry out functions of many conventional optical devicessuch as optical diffractive gratings, optical lenses, and opticalfilters, and other functions that may be difficult or impractical toachieve with conventional optical devices. Such grating patterns may befabricated in a wide range of materials, including metals such asaluminum, dielectric materials such as crystals (e.g., silicon) andnon-crystal materials (e.g., glasses, silica, plastics).

One advantageous feature of an optical holographic layer is that theoptical holographic layer may include different sets of holograms forsimultaneously performing different optical functions. For example, inone embodiment, a hologram for a lens function and a hologram for acolor filter function may be included in a single optical holographiclayer to operate independently from each other without interferencebetween the two. In comparison, conventional optical designs generallyrequire a microlens array and a separate filter array stacked over eachother and on top of the pixel array.

FIG. 1 shows a cross section of a portion of semiconductor imagingdevice 100 in accordance with a first embodiment. In FIG. 1, the imagingdevice 100 has an optical holographic layer 105 formed over a substrate101 of a suitable semiconductor material (for example, silicon). Theactive area of the substrate 101 has pixels 102 arranged in a1-dimensional or 2-dimensional array. In the FIG. 1 cross section,pixels are arranged in a Bayer pattern and the pixel row has analternating arrangement of blue and green pixels. Each pixel 102 has aphotoreceptor area 103, which absorbs input radiation, and other pixelcircuit elements for producing a pixel output signal. Imaging device 100also includes additional imager layers 104 such as a passivation layer,and interlevel dielectric (ILD) layers and associated metallizationlayers, which are fabricated to form pixel connection elements forconnections with the pixels and from the pixel array to peripheralcircuitry outside the array. The optical holographic layer 105 is formedover the upper surface of the additional layers 104. The hologram in theoptical holographic layer 105 is designed to operate as a lens to focusreceived light to the photoreceptor area 103 of each pixel 102 in thesubstrate 101 and also to filter colors of the input radiation such thateach pixel is associated with a particular color, for example, red,green, blue. An optical system, e.g., a main camera lens system, focusesthe input radiation onto holographic layer 105.

The hologram in the optical holographic layer 105 focuses and colorfilters the multiple incident beams 108 from the lens and respectivelydirects the output beams 106 to the photoreceptor areas 103 of differentpixels. The location of each photoreceptor area 103 may be in the centerof or offset from the center of each pixel 102. In the latter case, thehologram may be designed to focus the beam 108 at the 90 degree chiefray angle (CRA) to maximize photo collection efficiency. (See FIG. 3).

FIG. 2 shows a method of writing or recording the optical holographiclayer 105 in a semiconductor imaging device 100, in accordance with asecond embodiment described herein. Holographic writing or recordinguses a reference beam which is combined with light from an object beam,the reference beam and the object beam preferably emanating fromcoherent sources. Interference between the reference beam and the objectbeam, due to superposition of the light waves, produces a series ofintensity fringes that may be recorded on a holographic material, forexample, a photographic film. These fringes form a diffraction gratingon the film called the hologram.

Diffraction gratings that make up a hologram may be phase gratings oramplitude gratings. In phase gratings, the refractive index of theholographic material is modulated by exposure. In amplitude gratings,the absorption constant of the holographic material is modulated byexposure.

Referring to FIG. 2, an object light source 201 has specially createdcolor dot patterns in a 1-dimensional or 2-dimensional arraycorresponding to the pixels 102 in the semiconductor imaging device 100.Each color dot 202, 203 on the object light source 201 projects light toa corresponding area of layer 105 corresponding to respective colorpixel 213, 214 through an optical system 207, preferably comprising anoptical lens without aberrations. The semiconductor imaging device 100,the optical system 207 and the object light source 201 are aligned alongan optical axis 220, with the optical system 207 placed between theimaging device 100 and the object light source 201. The object lightsource 201 may project light simultaneously or sequentially with auser-defined time interval.

The object light beams 205 a-b, 206 a-b emanating from the correspondingcolor dots 202, 203 interfere with a reference light 204 at the opticalsystem 207. The reference light has red, green and blue components, oris light having wavelengths that are multiples of the red, green andblue components.

Light beams 208 a-b, 209 a-b pass through a respective elliptical area211, 212 on the optical hologram layer 105 to the respective pixels 213,214. The elliptical area 211, 212 is bigger than the area of the colorpixel itself resulting in an increase of about 2-10 times in quantumefficiency for collection of light. The overlap of the elliptical areas211, 212 corresponding to adjacent color pixels 213, 214 decreasescross-talk between color pixels because the interference of the incidentlight inside the hologram produces holographic deflected rays whichconverge to a center of a given pixel.

The optical system 207 is adjusted to focus each object light beam tothe photoreceptor areas 103 (FIG. 1) of the corresponding color pixel onthe semiconductor imaging device 100. For example, a red light emanatingfrom a red color dot interferes with the same wavelength reference lightwhen it passes through the optical holographic layer before beingprojected to a red pixel on the semiconductor imaging device. Theinterference between projected color dots light and the same colorreference light produces a hologram in the optical holographic layer. Inthis way, the hologram is written in the optical holographic layer foreach color separately, or for all colors simultaneously.

The location of each photoreceptor area 103 (FIG. 1) may be in thecenter of or offset from the center of each pixel 102 (FIG. 1). In thelatter case, the hologram may be designed to focus the beams 208 a-b atthe off-center location to maximize the collection efficiency.

The hologram formed in the optical hologram layer 105 is designed tooperate as a lens to focus received light to the photoreceptor area 103(FIG. 1) of each pixel 102 (FIG. 1) in the substrate 101 and also tofilter colors of the input radiation such that each pixel is associatedwith a particular color, for example, red, green, blue, duringsubsequent image capture operations. The hologram appears like a set ofmultiple grating patterns of elliptical size and each grating pattern isused to filter a specific color and to focus the filtered light to adesignated color pixel.

The optical holographic layer after recording appears to be the same asit was before recording or writing. However, a pattern of refractiveindex modulation is written on the optical holographic layer due toexposure.

FIG. 3 shows another embodiment of a method of recording an opticalholographic layer 105 in a semiconductor imaging device 100.

An object light source 201 has specially created color dot patterns in a1-dimensional or 2-dimensional array corresponding to the pixels 102 inthe semiconductor imaging device 100. Each color dot 202, 203 on theobject light source 201 projects light to a corresponding area of layer105 corresponding to respective color pixel 213, 214 through an opticalsystem 306 for the object light, preferably having an optical lenswithout aberrations, and an optical system for reference light 207. Thesemiconductor imaging device 100, the optical system 306 for the objectlight, the optical system for reference light 207, and the object lightsource 201 are aligned along an optical axis 220 with the optical system306 for the object light placed between the object light source 201 andthe optical system for reference light 207. The optical system forreference light 207 is placed between the semiconductor imaging device100 and the optical system 306 for the object light. The object lightsource 201 may project light simultaneously or sequentially with auser-defined time interval.

The object light beams 205 a-b, 206 a-b emanating from the correspondingcolor dots 202, 203 are refracted by the optical system 306 for objectlight. The refracted beams 321 a-b, 322 a-b interfere with a referencelight 204 at the optical system for reference light 207. The referencelight has red, green and blue components, or is light having wavelengthsthat are multiples of the red, green and blue components. The opticalsystem for reference light 207 may contain a concave semitransparentmirror for reflecting reference light and the optical system 306 forobject light may contain lenses for projecting refracted beams 321 a-b,322 a-b.

Light beams 208 a-b, 209 a-b pass through a corresponding ellipticalarea 211, 212 on the optical hologram layer 105 to the correspondingpixels 213, 214. The elliptical area 211, 212 is bigger than the area ofthe color pixel itself resulting in an increase of about 2-10 times inquantum efficiency for collection of light. The overlap of theelliptical areas 211, 212 corresponding to adjacent color pixels 213,214 decreases cross-talk between color pixels. In another embodiment,the elliptical areas 211, 212 may be circular.

The optical system 306 for object light is adjusted to focus each objectlight beam to the photoreceptor areas 103 (FIG. 1) of the correspondingcolor pixel on the semiconductor imaging device 100. For example, a redlight emanating from a red color dot is refracted by the optical system306 for object light, interferes with the reference light 207 and passesthrough the optical holographic layer 105 before being projected to ared pixel on the semiconductor imaging device 100. For example, a redlight emanating from a red color dot interferes with the same wavelengthreference light 207 when they pass through the optical holographic layer105 before being projected to a red pixel on the semiconductor imagingdevice 100. The interference between projected color dots light and thesame color reference light produces a hologram in the opticalholographic layer 105. In this way, a hologram is written in the opticalholographic layer 105 for each color separately, or for all colorssimultaneously.

The object light source 201, shown in FIG. 3, may use specially formedprofiling of light emission for each color dot. This specially formedlight emission may be spatially distributed and arranged such that theobject light is incident normally to the substrate 101. For example, redand green object light chief rays 215, 216 are at a normal angle to thesubstrate 101 resulting in a 90 degree chief ray angle for the projectedrefracted beams 321 a-b, 322 a-b.

The location of each photoreceptor area 103 (FIG. 1) may be in thecenter of or offset from the center of each pixel 102 (FIG. 1). In thelatter case, the hologram may be designed to focus the beams 209 a-b atthe off-center location to maximize the collection efficiency.

The hologram formed in the optical hologram layer 105 is designed tooperate as a lens to focus received light to the photoreceptor area 103(FIG. 1) of each pixel 102 (FIG. 1) in the substrate 105 and also tofilter colors of the input radiation such that each pixel is associatedwith a particular color, for example, red, green, blue during subsequentimage capture operations.

In another monochromatic embodiment, black and white holograms may berecorded or written onto holographic layer 105. In this method,reference light comprising an array of monochromatic light, for example,green color light, is projected onto the optical system, illustrated inFIGS. 2-3.

FIG. 4 shows a method of recording an optical holographic layer 105 in asemiconductor imaging device 100, in accordance with another embodiment.

An object light source 402 comprises a plurality of point monochromaticlight sources. The object light source 402 projects monochromatic lightthrough an optical system 207, preferably including an optical lenswithout aberrations. The semiconductor imaging device 100, the opticalsystem 207 and the object light source 402 are aligned along an opticalaxis 220, with the optical system 207 placed between the imaging device100 and the object light source 401.

The object light beams 403 a, 404 a emanating from the object lightsource 402 interfere with a reference light 204 from a reference lightsource 401 at the optical system 207. Light beams 403 b, 404 b passthrough a conical area 405 on the optical hologram layer 105.

After writing an optical holographic layer 105, using one of theabove-mentioned methods, the optical holographic layer 105 hasdiffraction grating patterns due to modulation of refraction index ofthe layer. This written optical holographic layer modulation appears asa “frozen” optical holographic layer pattern.

FIG. 5 illustrates an optical holographic layer 105, subsequent towriting using one of the above-mentioned methods, used to focus andcolor filter incident beams 108 from a lens and increasing quantumefficiency for collection of light. In a conventional imaging deviceusing a microlens and a color filter array, a red pixel adjacent to agreen pixel cannot collect red light incident on a portion of the colorfilter array corresponding to the green pixel. In contrast, the overlapof elliptical areas on the optical holographic layer 105 correspondingto adjacent color pixels 120, 121 results in the red pixel 121collecting red light 125 and the green pixel 120 collecting the greenlight 126 and thereby, increasing the collection of light.

FIG. 6 shows a method of capturing an image using a semiconductorimaging device 100 having a recorded optical holographic layer 105.Light 420 coming from an object 410 acts as a reference light for therecorded optical holographic layer 105. After passing through an opticalsystem 207, for example, a lens of a camera, a light beam 430 passesthrough the optical holographic layer 105. The optical holographic layer105 produces numerous color-filtered beams focused and directed torespective photosensors of pixels, as determined during the writing ofthe optical holographic layer 105.

When light passes through the optical holographic layer 105, thehologram filters the light into different colors and focuses thefiltered light to the designated color pixels, for example, red colorlight to red color pixel, green color light to green color pixels andblue color light to blue color pixels of a Bayer pixel array. Colorlight is not absorbed as is the case with color filter array (CFA) witha conventional pixel array. Therefore, all light reaches appropriatecolor pixels with little distortion. This increases the quantumefficiency for a given imaging device by approximately 2-10 times.

Pixel array employing a recorded optical holographic layer may be usedin an imaging device of the type depicted in FIG. 7. FIG. 7 illustratesa CMOS imaging device, although, as noted earlier, embodiments of theinvention may be used with other types of imaging devices employingother pixel array structures, such as CCD, for example.

FIG. 7 illustrates a block diagram of a CMOS imager device 700 having apixel array 701 with pixels 102. Pixel array 701 comprises a pluralityof pixels 102 arranged in a predetermined number of columns and rows.The pixels 102 of each row in array 701 are all turned on at the sametime by a row select line, and the pixels of each column are selectivelyoutput by respective column select lines. A plurality of row and columnlines are provided for the entire array 701. The row lines areselectively activated in sequence by the row driver 702 in response torow address decoder 703 and the column select lines are selectivelyactivated in sequence for each row activated by the column driver 704 inresponse to column address decoder 705. Thus, a row and column addressis provided for each pixel. The CMOS imager 700 is operated by thecontrol circuit 706, which controls address decoders 703, 705 forselecting the appropriate row and column lines for pixel readout, androw and column driver circuitry 702, 704, which apply driving voltage tothe drive transistors of the selected row and column lines. The pixeloutput signals typically include a pixel reset signal, Vrst, taken offthe floating diffusion node when it is reset and a pixel image signal,Vsig, which is taken off the floating diffusion node after chargesgenerated by an image are transferred to it. The Vrst and Vsig signalsare read by a sample and hold circuit 707 and are subtracted by adifferential amplifier 708 that produces a signal Vrst-Vsig for eachpixel, which represents the amount of light impinging on the pixels.This difference signal is digitized by an analog to digital converter709. The digitized pixel signals are then fed to an image processor 710to form a digital image. The digitizing and image processing can beperformed on or off the chip containing the pixel array 701.

FIG. 8 shows an image processor system 600, for example, a still orvideo digital camera system, which includes an imaging device 100,having a holographic layer 105 used as a lens and color separator. Theimaging device 100 may receive control or other data from system 600 andmay provide image data to the system. System 600 includes a processorhaving a central processing unit (CPU) 610 that communicates withvarious devices over a bus 660. For a camera, CPU 610 controls variouscamera functions. Some of the devices connected to the bus 660 providecommunication into and out of the system 600; one or more input/output(I/O) devices 640 and imaging device 100 are such communication devices.Other devices connected to the bus 660 provide memory, illustrativelyincluding a random access memory (RAM) 620, and one or more peripheralmemory devices such as a removable memory drive 650. A lens 695 is usedto allow an image to be focused onto the imaging device 100 when e.g., ashutter release button 690 is depressed. The imaging device 100 may becoupled to the CPU for image processing or other image handlingoperations. Non-limiting examples of processor systems, other than acamera system, which may employ the imaging device 100, include, withoutlimitation, computer systems, camera systems, scanners, machine visionsystems, vehicle navigation systems, video telephones, surveillancesystems, auto focus systems, star tracker systems, motion detectionsystems, image stabilization systems, and others.

While various embodiments of the invention have been described above, itshould be understood that they have been presented by way of example,and not limitation. It will be apparent to persons skilled in therelevant art that various changes in form and detail can be made.

I/We claim:
 1. An imaging device, comprising: an array of pixels, eachpixel configured to detect a color; and an optical layer including aplurality of diffraction gratings over the array of pixels, wherein eachdiffraction grating corresponds to a pixel of the array of pixels, eachdiffraction grating is configured to redirect a color component ofincident radiation to the corresponding pixel, and the redirected colorcomponent corresponds to the color that the corresponding pixel isconfigured to detect.
 2. The imaging device of claim 1, whereindiffraction gratings that correspond to adjacent pixels of the array ofpixels overlap one another.
 3. The imaging device of claim 2, whereinoverlapping diffraction gratings that correspond to pixels configured todetect different colors have different refractive indices.
 4. Theimaging device of claim 2, wherein overlapping diffraction gratings thatcorrespond to pixels configured to detect different colors havedifferent absorption constants.
 5. The imaging device of claim 1,wherein each diffraction grating has a larger area than a photoreceptorarea of the corresponding pixel.
 6. The imaging device of claim 1,wherein at least a first pixel has a photoreceptor offset from a centerof the first pixel, and wherein diffraction grating corresponding to thefirst pixel is configured to focus the color component of the incidentradiation to the photoreceptor at a 90° chief ray angle.
 7. The imagingdevice of claim 1, wherein each of the pixels includes a photoreceptorarea, and wherein each diffraction grating is configured to focus theredirected color component onto the photoreceptor area of thecorresponding pixel.
 8. The imaging device of claim 1, wherein theoptical layer is a planar layer.
 9. The imaging device of claim 1,wherein each diffraction grating is configured to redirect the colorcomponent of incident radiation to the corresponding pixel withoutabsorbing other color components of the incident radiation.
 10. Theimaging device of claim 1, wherein the plurality of diffraction gratingsinclude elliptical diffraction gratings.
 11. A CMOS imaging device,comprising: an array of pixels, each pixel configured to detect a color;a sample and hold circuit; and an image processor including an opticalfilter layer, wherein the optical filter layer has a plurality ofdiffraction gratings over the array of pixels, each diffraction gratingcorresponds to a pixel of the array of pixels, each diffraction gratingis configured to redirect a color component of incident radiation to thecorresponding pixel, and the redirected color component corresponds tothe color that the corresponding pixel is configured to detect.
 12. TheCMOS imaging device of claim 11, wherein diffraction gratings thatcorrespond to adjacent pixels of the array of pixels overlap oneanother.
 13. The CMOS imaging device of claim 11, wherein at least afirst pixel has a photoreceptor offset from a center of the first pixel,and wherein diffraction grating corresponding to the first pixel isconfigured to focus the color component of the incident radiation to thephotoreceptor at a 90° chief ray angle.
 14. The CMOS imaging device ofclaim 11, wherein each diffraction grating has a larger area than aphotoreceptor area of the corresponding pixel.
 15. The CMOS imagingdevice of claim 11, wherein each diffraction grating is configured toredirect the color component of incident radiation to the correspondingpixel without absorbing other color components of the incidentradiation.
 16. The CMOS imaging device of claim 11, wherein theplurality of diffraction gratings include elliptical diffractiongratings.
 17. A system, comprising: a lens; an imaging device configuredto receive incident light through the lens, the imaging device includingan array of pixel, each pixel configured to detect a color, and anoptical filter layer having a plurality of diffraction gratings over thearray of pixels, wherein: each diffraction grating corresponds to apixel of the array of pixels, each diffraction grating is configured toredirect a color component of incident radiation to the correspondingpixel, and the redirected color component corresponds to the color thatthe corresponding pixel is configured to detect.
 18. The system of claim17, wherein diffraction gratings that correspond to adjacent pixels ofthe pixel array overlap one another.
 19. The system of claim 17, whereineach diffraction grating has a larger area than a photoreceptor area ofthe corresponding pixel.
 20. The system of claim 17, wherein eachdiffraction grating is configured to redirect the color component ofincident radiation to the corresponding pixel without absorbing othercolor components of the incident radiation.